JPH0346895B2 - - Google Patents

Abstract

In a method of forming a video disc or a digital sound recording disc for example, a uniform layer of a predetermined thickness has to be applied to a substrate, and according to the invention, the layer material is applied in the form of a liquid with a known viscosity and the disc is rotated at a first velocity to spread the liquid and then the disc is rotated at a higher velocity to dry the liquid at least partly, to be in the form of a coating having a thickness which is dependent upon the viscosity of the liquid and the higher velocity at which the substrate is rotated. The method may be used is preparing a glass or other substrate for the application of a photoresist layer, or it may be used in the application of the photoresist layer, or in the application of a developer for developing an exposed photoresist layer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of molding video discs, and more particularly to a method of manufacturing a stamper for use in molding optically readable video disc masters and video disc replicas.

Optically readable video disk replicas are useful for storing large amounts of information, usually in the form of frequency modulated carrier signals, with high recording densities. The frequency modulated signal is typically recorded as a series of spaced pits or bumps arranged in a series of generally circular, concentric recording tracks.

Typically, a disk replica is molded using an injection molding device using a disk-shaped stamper obtained from a recording master. Typical recording masters are:
It includes a glass substrate with a disk-like flat surface, on which a thin recording layer, for example a metal film, is superimposed. Typically, information is recorded on the recording layer by focusing a brightness-modulated writing beam onto the recording layer using a radially movable objective lens while rotating the master at a predetermined speed. The intensity of this beam is modulated by a frequency modulated signal to alternately increase or decrease the intensity above a predetermined melting limit of the metal film, thereby forming a series of spaced pits in the metal film. . These pits and spacings preferably have a nominal shock factor of 50/50, thereby reducing the signal to the lowest Second harmonic distortion.
can be recorded.

The invention resides in a method for use in the production of video disc masters of the type having a photoresist recording layer, and in a method for manufacturing stampers from such masters. The master includes a glass substrate with a smooth, flat surface to which a thin, uniform recording layer of photoresist is deposited. A frequency modulated information signal is recorded in the photoresist recording layer using an intensity modulated writing beam, producing a series of spaced exposure areas arranged in a series of generally circular and concentric recording tracks.

In one aspect of the invention, the glass substrate is first primed by dispensing a fixative, such as stannous chloride, onto the surface of the substrate while rotating at a relatively low speed, e.g., about 75 to 100 rpm. . The surface is then rinsed with water, still rotating at the same speed, to remove any residual fixer, and then the cleaned surface is cleaned by rotating at a relatively high speed, e.g., about 750 to 1000 rpm. dry.

This method of preparing the substrate may include a preliminary step of polishing the substrate surface with a polishing agent of ultrafine molecular size and cleaning the polished surface. The cleaning step involves first cleaning the surface with a cleaning solution, then with water, drying by rotating the substrate at a relatively high speed, and wiping the surface with acetone to remove traces of dust and oil. It may also include the step of

In another feature of the invention, a photoresist recording layer is applied to the prepared surface of a glass substrate by dispensing a photoresist solution onto the surface of the glass substrate while rotating the substrate at a relatively low speed; Rotate at a relatively high speed to partially dry the photoresist solution to form a layer of approximately uniform thickness, and finally bake the photoresist-coated substrate in a predetermined manner to completely remove the photoresist layer. dry. The photoresist solution is preferably Shipley AZ1350 photoresist having a viscosity of about 1.3 centipoise, and the baking step preferably bakes the master at about 80° C. for about 20 minutes.

In another feature of the invention, a thin metal layer is formed on the glass substrate prior to application of the photosensitive recording layer. Another feature resides in the method of selecting the optimum peak brightness of the brightness modulated writing beam used to record the frequency modulated signal on the photoresist recording layer. In this case, a given test signal is first recorded on the disk in the form of a narrow series of recording tracks. Each set of tracks is recorded using a writing beam of different peak intensity. Since the photoresist layer is exposed whenever the intensity of the light beam exceeds a predetermined limit, a higher peak brightness will result in a longer length of exposed area. Thus, each set of recording tracks has a different shock coefficient.

In a preferred method, three or four sets of tracks are recorded, each having a different peak brightness in steps of about 5 percent. After development, which converts the exposed areas forming each track into a series of spaced pits, the disk is inspected to determine the particular set of tracks that have pits with a coefficient of impact closest to the optimum value. . The peak brightness of the light beam can be adjusted according to this determination and then a frequency modulated signal with an optimal impact coefficient can be recorded on the remaining unexposed portions of the photoresist layer.

The test signal preferably has a constant frequency and each set of recording tracks is preferably near the periphery of the photoresist layer. Also, each set preferably contains several hundred tracks and is separated from adjacent sets by a narrow unexposed band. Preferably, the developed photoresist layer is inspected by scanning each set of tracks with a reading beam to produce a reflected beam whose brightness is modulated according to the recorded pattern of spaced pits; detected and monitored using a spectrum analyzer.

In another feature of the invention, in order to develop the exposed photoresist layer, the layer is first pre-wetted with water while the substrate is rotated at a relatively low speed (e.g., 75-100 rpm) and then Water and a developer solution of a predetermined normality are applied to partially develop the layer, and finally only developer solution is applied for complete development. The developed photoresist layer is then washed with water to remove residual developer solution and finally rotated at a relatively high speed (preferably 750 to 1000 rpm) to dry the developed layer. The photoresist layer is preferably obtained from Shipley AZ1350 photoresist and the developer solution is preferably from about 0.230 to
It is either potassium hydroxide or sodium hydroxide with a normality of 0.240. In yet another feature of the invention, the step of applying both water and developer solution is about 5 to 10 seconds, the step of applying only developer is about 20 seconds, and the washing step is about 30 to 60 seconds.
Seconds.

Another feature of the invention is a technique for manufacturing stampers from developed recording masters for use in molding video disc replicas. In this feature, a first thin, uniform metal film is deposited on the developed recording layer, and then a second metal film is deposited on the first metal film.
Electroplating thin, uniform metal films to form an integral metal layer. The integral metal layer is then separated from the master and any residual photoresist material removed from the underside of the metal layer using a suitable solvent to form a stamper. The thickness of the first metal film is approximately 500 to
Preferably, the thickness of the second metal film is about 15 mils. Preferably, both metal films are made of nickel.

Many other features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

With reference to the drawings, particularly FIG.
A device for recording frequency modulated information is shown. The master includes a glass substrate 13 having a smooth, flat top surface onto which a predetermined uniform thickness of photoresist layer 15 is deposited. The photoresist layer is exposed by applying a light beam having a brightness exceeding a predetermined recording limit.

This recording device includes a writing laser 17, such as an argon ion laser, which generates a writing beam 19 having a predetermined brightness, and a brightness modulating beam 19 that modulates the brightness of the writing beam in accordance with a frequency modulated information signal received on line 23. A modulator 21 is included. Furthermore, the recording device
It includes a spindle motor 25 that rotates the recording master 11 at a predetermined angular velocity, and an objective lens 27 that focuses a brightness-modulated light beam onto the photoresist layer 15 of the recording master. The objective lens is mounted on a carriage (not shown) that is movable radially relative to the master so that the focused light beam traces a helical pattern on the photoresist layer.

As shown in FIGS. 2, 3 and 4, the brightness of the brightness-modulated light beam 19 is alternately greater and less than a predetermined recording limit of the photoresist layer 15, thereby producing a plurality of generally circular shapes. A series of spaced exposure areas 29 arranged in the form of concentric recording tracks 31 are formed in the layer. Each exposure area and the spacing from its neighbor are one frequency modulated symbol.
corresponds to a cycle. FIG. 5 shows the recording master 11 after development with the exposed areas removed and the master in a condition suitable for use in manufacturing a stamper.

The recording master 11 is first prepared for use with the recording apparatus of FIG. 1 through a special process. In this step, the top surface of the glass substrate 13 is first polished and then cleaned. Next, a photoresist solution is applied to this surface, and then a photoresist layer 15 is formed by drying and baking in a predetermined manner. After firing, the recording master is in a state suitable for recording. Another feature of the invention is to form a thin metal layer on the substrate prior to forming the photoresistor layer.

More specifically, the flat surface of the glass substrate 13 is first ground in the conventional manner using an aluminum oxide compound having a particle size of about 9 microns. Next, polish using ultrafine particle size zirconium oxide or cerium oxide polish. Cerium oxide has been found to be able to polish surfaces more quickly, but is generally difficult to clean.

The polished surface of glass substrate 13 is cleaned in a special three-step process. First, wash the surface with high-purity deionized water and scrub with a fine brush to remove most of the polish. Deionized water preferably has a resistance of 18 megaohm-cm. The cleaned surface of the glass substrate 13 is inspected with the naked eye under high-intensity light. Under this light, scratch-like defects and microscopic pits appear as point-like scattered light sources. If a defect is found, a microscope is used to measure its dimensions. If defects larger than 25 microns are detected, or if there is more than one defect per square millimeter smaller than 10 microns, the substrate is rejected and the polishing and cleaning process is repeated. Next, wipe the surface with acetone to remove any traces of dust or oil that may have been introduced during handling.

Second, the surface is cleaned with a detergent solution and third, about
Wash again with deionized water for 10-20 minutes.

After cleaning, the substrate 13 is placed on a turntable as shown in FIG. 6 and rotated at a rotation speed of approximately 750-1000 rpm to dry the surface. FIG. 6 shows an apparatus used to form a photoresist layer 15 on a cleaned substrate 13. The apparatus includes a variable speed motor 33 that rotates the substrate in a predetermined manner and three distribution tubes 3 that dispense deionized water, stannous chloride solution and photoresist solution in a predetermined sequence.
7, 39, 41 are mounted on the pivot arm 35.

The substrate 13 is first rotated at an angular velocity corresponding to about 75-100 rpm while dispensing the stannous chloride through the distribution tube 39 onto the cleaned top surface. The pivot arm 35 is rotated by hand to distribute the stannous chloride over the entire surface. It is believed that the stannous chloride molecules adhere to the cleaned surface of the substrate and assist in subsequent deposition of the photoresist solution.

Water is then applied to the surface through the distribution tube 37 to wash off any remaining stannous chloride solution and the motor 3
Increase the rotation speed in step 3 to approximately 750-1000 rpm to dry the cleaned surface. The surface is now in good condition for applying the photoresist solution.

The photoresist solution is prepared by diluting Shipley AZ1350 photoresist with Shipley AZ thinner, which is believed to contain cellosolve acetate, by an approximately 3 to 1 ratio. This solution has a viscosity of about 1.3 centipoise and is filtered to remove particles larger than about half a micron. Viscosity can be measured by standard techniques, for example by a Canon-Finske viscometer.

Next, add this diluted photoresist solution to approx.
The tube 41 is applied to the prepared top surface of the substrate 13 rotating at 75-100 rpm. Again, pivot arm 35 is manually rotated to distribute solution across the entire radius of the substrate. At speeds below about 75 rpm, a film of approximately uniform thickness can be obtained over a relatively long period of time, but this increases the tendency for layer contamination. On the other hand, at speeds above 100 rpm, radial streaks and flow patterns occur;
This may have a negative impact on the quality of subsequent information recording. Approximately 35 ml of photoresist solution is required to completely cover a substrate having a diameter of approximately 35.56 cm.

After covering the surface of the substrate 13 with the photoresist solution, the rotational speed of the motor 33 is increased to approximately 750°C until drying.
- Increases to 1000rpm. This makes it possible to obtain the photoresist layer 15 with a predetermined uniform thickness.

Once the thickness of the photoresist layer 15 is found to be inversely proportional to revolutions per minute (rpm) and temperature, the substrate can be rotated to adjust a specific rotational speed that partially dries the photoresist solution. A predetermined thickness can be obtained. for example,
Appropriate rotational speeds can be measured in the usual manner using a Tolansky interferometer. This technique can indicate the relative thickness of the layers, and through an iterative process of continuously adjusting the rotation speed, the optimal rotation speed can be determined. If the viscosity and temperature of the photoresist solution can be maintained approximately uniform, this rotational speed adjustment may only be made occasionally. It is currently preferred that the layer thickness be approximately 1150 to 1350 Å, so that the disk replica produced will have information-bearing bumps or pits of corresponding height.

If the dried photoresist layer 15 is found to have any defects (eg, radial streaks, extraneous particles), the layer can be removed using a suitable solvent such as Shipley AZ thinner. A new layer can then be applied as described above.

After removal from the turntable of FIG. 6, recording master 11 is baked to completely dry photoresist layer 15 and maximize exposure tolerance. The masters are preferably baked for about 20 minutes at about 80°C; these parameters are kept to tight tolerances to minimize variations in exposure tolerances when sequentially recording information on a large number of recording masters. must be preserved.

Since the exposure sensitivity of each recording master tends to be slightly different from the others, it is desirable to optimize the peak brightness of the brightness modulated light beam 19 (FIG. 1) for each master. Able to record frequency modulated information signals with an impact factor of 50. According to another feature of the invention, a predetermined test signal is recorded on each master 11 in the form of a plurality of sets of adjacent recording tracks, each set being recorded at a different peak brightness. After developing the test signal using the development technique described in detail below, the recorded master is inspected to determine the particular set of tracks with the shock coefficient closest to the desired 50/50 value. After determining the optimal peak brightness in this manner, the frequency-converted information signal can be recorded on the remaining unexposed portions of the recording master with the optimal impact coefficient.

The test signal preferably has a constant frequency of about 7-8 MHz and is preferably recorded on three or four sets of tracks, each set having a peak intensity varying by about 5 percent.
Each set is recorded for approximately 10 seconds, which corresponds to several hundred recording tracks. Preferably, these sets are separated by a narrow band of unexposed portions of the photoresist layer 15 and located in a narrow area near the inner periphery of the layer.

These sets of developed recording tracks can be inspected by scanning each set with a reading beam (not shown) and producing a reflected beam with an intensity modulated according to the recorded test signal. . This reflected light beam is intensity modulated. This is because the reflectance of the unexposed portion of the photoresist layer 15 is approximately 4 percent, and the reflectance of other portions is approximately zero. The modulated beam is suitably detected and monitored with a conventional spectrum analyzer for the presence of second harmonic distortion. This distortion means that the test signal is optimally 50/5
Minimum when recorded at 0 impact coefficient.

It is not necessary for the reading beam to follow each recording track of each set of tracks. This is because the same test signal is recorded on adjacent tracks. Note, however, that the eccentricity of recorded master 11 ensures that the reading beam does not scan more than one set of tracks at a time. The reading beam is preferably generated by a helium-neon laser. This is because the wavelength does not expose the photoresist layer 15.

Using the recording apparatus of FIG. 1, a frequency-modulated information signal is recorded on the remaining unexposed portions of the photoresist layer 15 with the peak brightness of the writing beam 19 adjusted to an optimum value. Next, this recorded master 1
1 is developed to convert each recording track into a series of spaced pits of uniform depth, width, and continuously varying length.

In yet another feature of the invention, the exposed recording master 11 is developed in a special process. In this process, a series of fluids are dispensed while the master is rotated by a turntable of the type shown in FIG. 6 at a speed of approximately 75-100 rpm. The process involves first dispensing water to pre-wet the layer, then dispensing water and a developer solution of a given normality to partially develop the layer, and finally dispensing only the developer solution. and then perform complete development. The developed photoresist layer is then washed with water to remove residual developer solution, after which the master rotation speed is increased to about 750-1000 rpm to dry the developed layer.

Preferred developer solutions are selected from the group including potassium hydroxide, sodium hydroxide, and have a normality of about 0.230 to 0.240. Preferably, the step of dispensing the water and developer solution takes about 5 to 5 minutes.
10 seconds, and the stage of dispensing only the developer solution is approx.
20 seconds and the wash step is about 30-60 seconds.

A stamper suitable for molding a video disc replica is a developed recording master 11.
make from In another feature of the invention, in making the stamper, the photoresist recording layer 15 is first coated with approximately
Deposit a uniform metal film with a thickness of 500−600A゜, then
A second uniform metal film approximately 15 mils thick is electroplated onto this first metal film. The underside of the first film conforms exactly to the pattern of spaced pits formed in the photoresist layer, and the two films become an integral metal layer. The integral metal layer is separated from the recording master and any residual photoresist material is removed using a suitable photoresist thinner to form a stamper. In a preferred embodiment, both metal films are made of nickel.

As can be seen from the foregoing description, the present invention provides a number of novel techniques for use in effectively manufacturing recording masters. The master includes a photoresist recording layer capable of recording frequency modulated information signals with high signal-to-noise ratio and density. In another feature of the invention, metal stampers used to mold replicas of the masters are made from these recorded masters.

Although the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that various changes can be made without departing from the spirit or scope of the invention. Accordingly, it is not intended that the invention be limited except as by the claims.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus for recording a frequency-modulated information signal on a recording master made according to the method of the present invention, and FIG. 2 is an enlarged plan view of a part of the recording master shown in FIG. FIG. 3 is a graph showing the modulated intensity of the writing beam in the recording device of FIG. 1; FIG. A cross-sectional view of a part of the recording master along the recording track.
FIG. 3 shows the photoresist recording layer exposed whenever the brightness of the writing beam exceeds a predetermined limit; FIG. 5 shows the photoresist recording layer after development with the exposed areas removed;
FIG. 4 is a sectional view of the recording master, and FIG. 6 is a perspective view of a turntable used to form a photoresist recording layer on the recording master of FIG. 1. 11...Recording master, 13...Glass substrate, 1
5... Photoresist layer, 17... Writing laser,
25...Motor, 27...Objective lens, 29...
Exposure area, 31... Recording track, 33... Motor, 35... Pivot arm, 37, 39, 41
...Distribution tube.

Claims (1)

[Claims] 1. A method of coating a photoresist layer with a predetermined uniform thickness on a glass substrate used for molding an optical disk master, the method comprising: preparing a glass substrate with a flat surface, and applying a photoresist layer with a predetermined viscosity to a glass substrate with a predetermined uniform thickness. dispensing a predetermined amount of photoresist onto the surface while rotating the glass substrate at a first predetermined speed, and rotating the glass substrate coated with the photoresist at a second predetermined speed. drying the photoresist to a predetermined degree of dryness to form a layer of photoresist having a uniform thickness determined by the initial viscosity of the photoresist and a second predetermined rate; A method of applying a photoresist layer comprising the step of baking the photoresist-coated substrate at a predetermined temperature for a predetermined time to completely dry the photoresist layer. 2. In the method described in claim 1,
The selected photoresist has a viscosity of about 1.3 centipoise, and in the firing step, the predetermined temperature is about 80°C and the predetermined time is about
A method of applying a photoresist layer, characterized in that it takes 20 minutes. 3. In the method described in claim 1,
The first predetermined speed is in the range of about 75 rpm to 100 rpm, and the second predetermined speed is in the range of about 750 rpm to 1000 rpm.
A method of applying a photoresist layer characterized in that the photoresist layer is in the range of .